1. Field of the Invention
The present invention relates to a chopper type boosting switching regulator.
2. Description of the Related Art
A conventional boosting switching regulator will be described. FIG. 2 is a block diagram showing a conventional boosting switching regulator.
In the boosting switching regulator, a transistor Q11 that is controlled by a buffer 181 turns off, a transistor Q12 that is controlled by a buffer 182 turns on, and a current from an input power supply 35 flows into a ground through a coil L10 and the transistor Q12. In this stage, energy is accumulated in the coil L10. Thereafter, after the transistor Q12 turns off, the transistor Q11 turns on, and the energy that has been accumulated in the coil L10 is accumulated in a capacitor C10 that is connected to an output terminal through the transistor Q11. An output voltage VOUT of the output terminal is transmitted to a control circuit 18 through a resistor (not shown), and the control circuit 18 controls the transistor Q11 and the transistor Q12 so as to hold the output voltage VOUT at a constant voltage higher than an input voltage VDD of the input power supply 35 on the basis of the transmitted voltage (for example, refer to JP 2005-160198 A).
The buffer 181 outputs a voltage that swings between the input voltage VDD and the output voltage VOUT to the transistor Q11, and the buffer 182 outputs a voltage that swings between the input voltage VDD and a ground voltage to the transistor Q12.
Also, a back gate voltage of the transistor Q11 is the output voltage VOUT.
However, in the conventional boosting switching regulator, when the input voltage VDD is applied while boosting operation is stopped, there is a possibility that the output voltage VOUT based on the input voltage VDD is output by the aid of the coil L10 and a parasitic bipolar transistor of the transistor Q11 whose back gate voltage is indefinite.
Also, in the case where the output voltage VOUT is not output while the boosting operation is stopped, because the power is not supplied to the buffer 181, there is a possibility that the transistor Q11 turns on. When the input voltage VDD is applied, there is the possibility that the output voltage VOUT based on the input voltage VDD is output by the aid of the coil L10 and the transistor Q11.